I don't understand how this forum works. But here goes. I'm also interested in the science behind the carbs in yogurt.

Re the methods: This is I think what Dr. Goldberg used:

Enzymic methods for the measurement of lactose are well known and are generally based on the hydrolysis of lactose to D-galactose and D-glucose with β-galactosidase followed by determination of either D-galactose or D-glucose. In the International Dairy Federation Methods(79B:1991) for the measurement of lactose in “dried milk, dried ice-mixes & processed cheese”, details are given for deproteinisation of samples, hydrolysis of lactose with β-galactosidase and measurement of either released D-galactose or D-glucose


http://216.239.51.104/search?q=cach...ctosidase&hl=en

See above for full details.

The important thing to understand is that the bacteria take up the lactose whole. Then the enzymes inside the bacteria split the lactose into glucose and galactose and metabolize them into lactic acid. Glucose and galactose can be interconverted in many species. How much conversion goes on probably depends on the species of bacterium, which varies a lot from brand to bran.

See the Danon site for a picture of this: http://www.danonevitapole.com/extra...ile/DWN02US.pdf

The carb content of the yogurt *will* vary depending on what you start with and how long you ferment it. Commercial yogurt sits around a long time before you buy it, and even if it is kept cool, some fermentation continues. Commercial yogurt usually has milk solids added and hence starts off with more lactose.

This URL gives lactose values as low as 4.

http://www.nationaldairycouncil.org...cts/table10.pdf

I would assume that the rest of the lactose had been taken up by the bacteria, hydrolyzed by beta-galactosidase into glucose and galactose, and then further metabolized (broken down). Note that this is different from Lactaid milk, in which you use the same (or a similar) enzyme to break the lactose into glucose and galactose, but there are no bacteria to break those sugars down into lactic acid so the carb count doesn't change.

Yogurt has a very low GI. I think it's about 14, with a glucose load of 2, so I think the lower numbers are reasonable.